Soluble guanylate cyclase (sGC) is a receptor for nitric oxide (NO) which is found in the cytoplasm of many cell types. In humans, functional sGC is a heterodimer composed of either an alpha 1 or alpha 2 subunit combined with the beta 1 subunit which has a heme prosthetic group. Under non-pathophysiological conditions, NO binding to the heme of sGC activates the enzyme to catalyze the conversion of guanosine-5′-triphosphate (GTP) to cyclic guanosine monophosphate (cGMP). cGMP is a second messenger which exerts effects by modulating cGMP dependent protein kinase (PKG) isoforms, phosphodiesterases, and cGMP gated ion channels. In doing so, sGC has been demonstrated to modulate numerous pathways associated with diseases including arterial hypertension, pulmonary hypertension, atherosclerosis, heart failure, liver cirrhosis, renal fibrosis, and erectile dysfunction (O. Evgenov et al., Nature Reviews, 2006, 5, 755-768 and Y. Wang-Rosenke et al., Curr. Med. Chem., 2008, 15, 1396-1406).
Under normal conditions, the iron in sGC exists in the ferrous state which is capable of binding to NO and carbon monoxide (CO). However, under conditions of oxidative stress which can occur in various diseases, published reports indicate that the heme iron becomes oxidized to the ferric state which is incapable of being activated by NO or CO. The inability of NO to signal through sGC with an oxidized heme iron has been hypothesized to contribute to disease processes. Recently, two novel classes of compounds have been described which potentiate sGC activity in a heme dependent (sGC stimulators) and heme independent (sGC activators) manner. The activity of sGC stimulators synergizes with NO to increase cGMP production while sGC activators are only additive with NO to augment cGMP levels (O. Evgenov et al., Nature Reviews, 2006, 5, 755-768). Both stimulators and activators of sGC have demonstrated benefit in animal models of disease. Activators of sGC provide the advantage of being able to preferentially target the diseased, non-functional form of the enzyme. sGC activators include BAY 58-2667 (cinaciguat) (J-P Stasch et al., Brit J. Pharmacol., 2002, 136, 773-783) and HMR-1766 (ataciguat) (U. Schindler et al., 2006, Mol. Pharmacol., 69, 1260-1268).
NO has an important role in maintaining normal cellular and tissue function. However, adequate signaling in the NO pathway can be disrupted at a number of steps. NO signaling can be impaired by reduced levels of nitric oxide synthase (NOS) enzymes, NOS activity, NO bioavailability, sGC levels, and sGC activity. sGC activators have the potential to bypass the functional impediment produced by all of these impairments. Since sGC activation occurs downstream of NO synthesis or NO availability, these deficiencies will not impact the activity of sGC activators. As described above, the activity of sGC in which function is disrupted by heme iron oxidation will be corrected by sGC activators. Thus, sGC activators have the potential to provide benefit in many diseases caused by defective signaling in the NO pathway.
Activation of sGC has the potential to provide therapeutic benefit for atherosclerosis and arteriosclerosis. Cinaciguat treatment has been demonstrated to prevent neointimal hyperplasia after endothelial denudation by wire injury of the carotid artery in rats (K. Hirschberg et al., Cardiovasc. Res., 2010, 87, Suppl. 1, S100, Abstract 343). Ataciguat inhibited atherosclerotic plaque formation in ApoE−/− mice feed a high fat diet (M. van Eickels, BMC Pharmacology, 2007, 7, Suppl. 1, S4). Decreased NO production in endothelial nitric oxide synthase (eNOS) deficient mice increased vascular inflammation and insulin resistance in response to nutrient excess. In the same study, the phosphodiesterase 5 (PDE5) inhibitor sildenafil reduced vascular inflammation and insulin resistance in mice fed a high-fat diet (N. Rizzo et al., Arterioscler. Thromb. Vasc. Biol., 2010, 30, 758-765). Lastly, after balloon-injury of rat carotid arteries in vivo, a sGC stimulator (YC-1) inhibited neotima formation (C. Wu, J. Pharmacol. Sci., 2004, 94, 252-260
The complications of diabetes may be reduced by sGC activation. Glucose induced suppression of glucagon release is lost in pancreatic islets that lack PKG, thus suggesting a role of sGC mediated cGMP production in glucose regulation (V. Leiss et al., BMC Pharmacology, 2009, 9, Suppl. 1, P40).
It is well established clinically that elevation of cGMP by treatment with PDE5 inhibitors is efficacious for the treatment of erectile dysfunction (ED). However, 30% of ED patients are resistant to PDE5 inhibitor treatment (S. Gur et al., Curr Pharm. Des., 2010, 16, 1619-1633). The sGC stimulator BAY-41-2272 is able to relax corpus cavernosum muscle in a sGC dependent manner, thus suggesting that increased sGC activity could provide benefit in ED patients (C. Teixeira et al., J. Pharmacol. & Exp. Ther., 2007, 322, 1093-1102). Furthermore, sGC stimulators and sGC activators used individually or either in combination with PDE5 inhibitor was able to treat ED in animal models (WO 10/081,647).
There is evidence that sGC activation may be useful in preventing tissue fibrosis, including that of the lung, liver, and kidney. The processes of epithelial to mesenchyal transition (EMT) and fibroblast to myofibroblast conversion are believed to contribute to tissue fibrosis. When either cincaciguat or BAY 41-2272 was combined with sildenafil, lung fibroblast to myofibroblast conversion was inhibited (T. Dunkern et al., Eur. J. Pharm., 2007, 572, 12-22). NO is capable of inhibiting EMT of alveolar epithelial cells (S. Vyas-Read et al., Am. J. Physiol. Lung Cell Mol. Physiol., 2007, 293, 1212-1221), suggesting that sGC activation is involved in this process. NO has also been shown to inhibit glomerular TGF beta signaling (E. Dreieicher et al., J. Am. Soc. Nephrol., 2009, 20, 1963-1974) which indicates that sGC activation may be able to inhibit glomerular sclerosis. In a pig serum model and carbon tetrachloride model of liver fibrosis, an sGC activator (BAY 60-2260) was effective at inhibiting fibrosis (A. Knorr et al., Arzneimittel-Forschung, 2008, 58, 71-80).
Clinical studies have demonstrated efficacy using the sGC activator cinaciguat for the treatment of acute decompensated heart failure (H. Lapp et al., Circulation, 2009, 119, 2781-2788). This is consistent with results from a canine tachypacing-induced heart failure model in which acute intravenous infusion of cinaciguat was able to produce cardiac unloading (G. Boerrigter et al., Hypertension, 2007, 49, 1128-1133). In a rat myocardial infarction induced chronic heart failure model, HMR 1766 improved cardiac function and reduced cardiac fibrosis which was further potentiated by ramipril (F. Daniela, Circulation, 2009, 120, Suppl. 2, S852-S853).
Activators of sGC can be used to treat hypertension. This has been clearly demonstrated in clinical studies in which the dose of cinaciguat is titrated based on the magnitude of blood pressure reduction achieved (H. Lapp et al., Circulation, 2009, 119, 2781-2788). Preclinical studies using cinaciguat had previously shown the ability of sGC activation to reduce blood pressure (J.-P. Stasch et al., 2006, J. Clin. Invest., 116, 2552-2561). Similar findings have been reported using the sGC activator HMR 1766 as well (U. Schindler et al., 2006, Mol. Pharmacol., 69, 1260-1268).
The activation of sGC has the potential to reduce inflammation by effects on the endothelium. BAY 41-2272 and a NO donor inhibited leukocyte rolling and adhesion in eNOS deficient mice. This was demonstrated to be mediated by down-regulation of expression of the adhesion molecule P-selectin (A. Ahluwalla et al., Proc. Natl. Acad. Sci. USA, 2004, 101, 1386-1391). Inhibitors of NOS and sGC were shown to increase endotoxin (LPS) induced ICAM expression on mesenteric microcirculation vessels. This was reduced by an NO donor in a cGMP dependent manner. Treatment of mice with NOS or sGC inhibitors increased neutrophil migration, rolling, and adhesion induced by LPS or carrageenen (D. Dal Secco, Nitric Oxide, 2006, 15, 77-86). Activation of sGC has been shown to produce protection from ischemia-reperfusion injury using BAY 58-2667 in both in vivo and in an isolated heart model (T. Krieg et al., Eur. Heart J., 2009, 30, 1607-6013). Similar results were obtained using the same compound in a canine model of cardioplegic arrest and extracorporeal circulation (T. Radovits et al., Eur J. Cardiothorac. Surg., 2010).
Some studies have indicated the potential of sGC activation to have antinociceptive effects. In streptozotocin-induced diabetes models of nociception in mice (writhing assay) and rats (paw hyperalgesia), elevation of cGMP levels by administration of sildenafil blocked the pain response, which in turn was abrogated by a NOS or sGC inhibitor (C. Patil et al., Pharm., 2004, 72, 190-195). The sGC inhibitor 1H-1,2,4.-oxadiazolo-4,2-a.quinoxalin-1-one (ODQ) has been demonstrated to block the antinociceptive effects of various agents including meloxicam and diphenyl diselenide in a formalin induced pain model (P. Aguirre-Banuelos et al., Eur. J. Pharmacol., 2000, 395, 9-13 and L. Savegnago et al., J. Pharmacy Pharmacol., 2008, 60, 1679-1686) and xylazine in a paw pressure model (T. Romero et al., Eur. J. Pharmacol., 2009, 613, 64-67). Furthermore, ataciguat was antinociceptive in the carrageenan model of inflammatory triggered thermal hyperalgesia and the spared nerve injury model of neuropathic pain in mice (WO 09/043,495).
Inhibition of PDE9, a phosphodiesterase specific for cGMP expressed in the brain, has been shown to improve long-term potentiation (F. van der Staay et al., Neuropharmacol. 2008, 55, 908-918). In the central nervous system, sGC is the primary enzyme which catalyzes the formation of cGMP (K. Domek-Lopacinska et al., Mol. Neurobiol., 2010, 41, 129-137). Thus, sGC activation may be beneficial in treating Alzheimer's and Parkinson's disease. In a phase II clinical study, the sGC stimulator riociguat, was efficacious in treating chronic thromboembolic pulmonary hypertension and pulmonary arterial hypertension (H. Ghofrani et al., Eur. Respir. J., 2010, 36, 792-799). These findings extend the preclinical studies in which BAY 41-2272 and cinaciguat reduced pulmonary hypertension in mouse (R. Dumitrascu et al., Circulation, 2006, 113, 286-295) and lamb (O. Evgenov et al., 2007, Am. J. Respir. Crit. Care Med., 176, 1138-1145) models. Similar results were obtained using HMR 1766 in a mouse model of pulmonary hypertension (N. Weissmann et al., 2009, Am. J. Physiol. Lung Cell. Mol. 297, L658-665).
Activation of sGC has the potential to treat chronic kidney disease. Both BAY 58-2667 and HMR 1766 improved renal function and structure in a rat subtotal nephrectomy model of kidney disease (P. Kalk et al., 2006, Brit. J. Pharmacol., 148, 853-859 and K. Benz et al., 2007, Kidney Blood Press. Res., 30, 224-233). Improved kidney function and survival was provided by BAY 58-2667 treatment in hypertensive renin transgenic rats (TG(mRen2)27 rats) treated with a NOS inhibitor (J.-P. Stasch et al., 2006, J. Clin. Invest., 116, 2552-2561). BAY 41-2272 treatment preserved kidney function and structure in a chronic model of kidney disease in rats induced by uninephrectomy and anti-thyl antibody treatment (Y. Wang et al., 2005, Kidney Intl., 68, 47-61). Diseases caused by excessive blood clotting may be treated with sGC activators. Activation of sGC using BAY 58-2667 was capable of inhibiting platelet aggregation induced by various stimuli ex vivo. Additionally, this compound inhibited thrombus formation in vivo in mice and prolonged bleeding time (J.-P. Stasch et al., 2002, Brit. J. Pharmacol., 136, 773-783). In another study using HMR 1766, in vivo platelet activation was inhibited in streptozotocin treated rats (A. Schafer et al., 2006, Arterioscler. Thromb. Vasc. Biol., 2006, 26, 2813-2818).
sGC activation may also be beneficial in the treatment of urologic disorders (WO/08138483). This is supported by clinical studies using the PDE5 inhibitor vardenafil (C. Stief et al., 2008, Eur. Urol., 53, 1236-1244). The soluble guanylate cyclase stimulator BAY 41-8543 was able to inhibit prostatic, urethra, and bladder smooth muscle cell proliferation using patient samples (B. Fibbi et al., 2010, J. Sex. Med., 7, 59-69), thus providing further evidence supporting the utility of treating urologic disorders with sGC activators.
The above studies provide evidence for the use of sGC activators to treat cardiovascular diseases including hypertension, atherosclerosis, peripheral artery disease, restenosis, stroke, heart failure, coronary vasospasm, cerebral vasospasm, ischemia/reperfusion injury, thromboembolic pulmonary hypertension, pulmonary arterial hypertension, stable and unstable angina, thromboembolic disorders. Additionally, sGC activators have the potential to treat renal disease, diabetes, fibrotic disorders including those of the liver, kidney and lungs, urologic disorders including overactive bladder, benign pro static hyperplasia, and erectile dysfunction, and neurological disorders including Alzheimer's disease, Parkinson's disease, as well as neuropathic pain. Treatment with sGC activators may also provide benefits in inflammatory disorders such as psoriasis, multiple sclerosis, arthritis, asthma, and chronic obstructive pulmonary disease.